PROPERTY, PLANT AND EQUIPMENT (Value Of Each Of The Major Classes Of Consolidated Depreciable Assets) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 13,216.0	$ 13,044.7
Allowance for depreciation and depletion	(2,026.4)	(1,837.4)
Property, plant and equipment, net	11,189.6	11,207.3
Land Rights And Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,807.6	7,920.8
Office And Information Technology [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	118.8	92.4
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	184.9	162.0
Mining Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,401.3	1,290.7
Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,069.5	1,937.4
Railroad Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	218.9	240.8
Electric Power Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	62.1	58.7
Port Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	100.7	114.3
Interest Capitalized During Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	23.1	20.8
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	60.0	43.9
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	37.5	39.0
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,131.6	$ 1,123.9